1. Field of the Invention
The present invention relates to a thin-film magnetic head for applying to a magnetic recording technique in which the head writes/reads data to/from a magnetic recording medium, especially to a thin-film magnetic head for applying to perpendicular magnetic recording. The present invention further relates to a head gimbal assembly (HGA) provided with the thin-film magnetic head, and a magnetic recording and reproducing apparatus provided with the HGA.
2. Description of the Related Art
In recent years, perpendicular magnetic recording has been actively developed instead of conventional longitudinal magnetic recording to realize more improvement in a real recording density of magnetic recording and reproducing apparatuses, especially magnetic disk drive apparatuses. In the perpendicular magnetic recording, demagnetization field drastically decreases in a magnetization transition region between record bits on a magnetic recording medium, and therefore, the magnetization transition width can become much smaller than that of the longitudinal magnetic recording. Furthermore, the record bit formed by the perpendicular magnetic recording is not greatly affected by a thermal fluctuation that becomes serious problem for achieving higher recording density in the longitudinal magnetic recording. As described above, the perpendicular magnetic recording has a potential to realize more stable and higher recording density, and therefore, thin-film magnetic heads for applying to the perpendicular magnetic recording have been developed intensively.
In the thin-film magnetic head for the perpendicular magnetic recording, a shielded pole structure is recently adopted, which includes a main magnetic pole, an auxiliary magnetic pole as a return yoke, and a write coil for exciting magnetic flux in these magnetic poles. Whereas, the corresponding magnetic recording medium mainly has a stacked structure of a soft-magnetic backing layer for acting as a part of magnetic circuit and a perpendicular recording layer. In some cases using this magnetic recording medium, an external magnetic field is likely to cause a phenomenon in which unwanted writing or erasing of data occur in positions distant from the track to be written. This phenomenon is thought to be derived from that, under the condition of applying the external field to the head, a rather large loop of magnetic flux is generated through the soft-magnetic backing layer and the auxiliary magnetic pole. The magnetic flux of the generated loop has a tendency to concentrate near both ends of the edge on the air bearing surface (ABS) side of the auxiliary magnetic pole, which reaches the head end surface. As a result, magnetic fields generated from the flux-concentrating portions may be likely to cause unwanted writing or erasing.
A magnetoresistive (MR) element provided in the head for reading data usually has upper and lower shields sandwiching an MR multilayer, which is a magneto-sensitive part, between them. In some cases, the upper and lower shields may contribute to the formation of the above-described magnetic flux loop, and magnetic fields generated near both ends of the edge of these shields are likely to cause unwanted writing or erasing.
As a measure for avoiding the unwanted writing or erasing due to the external magnetic field and for improving the tolerance to external magnetic field, Japanese Patent Publication No. 2006-114160A describes an auxiliary magnetic pole, a lower shield or an upper shield which has a concave portion provided on the side opposite to ABS or has a recess from the head end surface on the ABS side at both end portions in the track width direction. This structure with the concave portion or the recess is intended to reduce a leakage magnetic field from the end portions of the auxiliary magnetic pole, the lower shield or the upper shield. Further, US Patent Publication 2006/0092565A1 describes a magnetic structure having a forward projecting portion extending toward ABS and the first and second side wing portions extending from the forward projecting portion along the transverse direction (the track width direction). The publication argues that even if magnetic flux concentrates at the end portion in the track width direction of the side wing portion, the concentrating portion is sufficiently distant from the ABS; therefore, unwanted writing or erasing to the medium can be avoided. Further, Japanese Patent Publication No. 2004-39148A describes a return yoke layer (an auxiliary magnetic pole layer) having tapered surfaces at both end portions in the track width direction. The publication argues that there exist no angles to cause the concentration of magnetic flux in the return yoke layer; therefore, unwanted writing or erasing to the medium can be avoided.
However, these prior techniques cannot correspond to the recent requirement for reducing the area of the upper and lower shields of the MR element.
Recently, to improve the sensitivity of magnetic field in the MR element, a current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) element or a tunnel magnetoresistive (TMR) element has been adopted. In these elements, the shields also act as electrodes, that is, upper and lower shields (electrodes) sandwich an MR multilayer and further an insulating layer for preventing short-circuiting of the sense current. This sandwich structure causes the considerable amount of stray capacitance. This stray capacitance may be likely to cause a noise in the read output of the MR element; therefore, the area of the upper and lower shields is now intended to be set smaller in order to reduce the stray capacitance. Further, even in the case that a current-in-plane giant magnetoresistive (CIP-GMR) element is used as the MR element, the reduction of the areas of shields is also required with the purpose of miniaturizing the head.
However, under the condition that the shields have smaller areas, it is difficult to form the above-described concave portion, the recess portion, the forward projecting portion, the side wing portion, the taper portion and so on with a sufficiently large size. That is, it has been quite difficult to adopt a design for improving the tolerance of external magnetic field into the shield with smaller area.